PROJECT 1 - Human Fetal Liver and the Metabolic Syndrome. The purpose of this project is to develop and employ a model for studying the effects of arsenic on fetal liver development. The project is predicated on the relationship between altered fetal liver development and risk for metabolic syndrome in the offspring. The role of the liver In metabolic regulation and insulin sensitivity is well established. The association between intrauterine growth retardation, fetal metabolic programming and metabolic syndrome in the offspring is also established, having been shown in recent years to involve epigenetic mechanisms. The goal of this project is to develop a model in which human fetal liver is xenografted to nude rats. We will use this model to test the hypothesis that, like alterations in the nutrient environment, fetal arsenic exposure induces epigenetic changes in fetal liver that predispose to metabolic syndrome in the adult The proposal is based on published evidence that fetal arsenic exposure induces epigenetic changes in fetal liver. The proposal also derives from our extensive characterization of growth-regulating signaling mechanisms in the fetal rat and our identification of novel biomarkers for the fetal hepatocyte phenotype. We have shown that late term fetal hepatocytes, unlike adult rat hepatocytes, show mitogenindependent proliferation and are resistance to the anti-proliferative effects of rapamycin, an inhibitor of the nutrient-sensing mTOR pathway. The aforementioned biomarkers include a number of proteins involved in growth factor signaling, cell cycle control and translation control. We have also observed that rapamycin-induced inhibition of mTOR modulates gene expression in a manner most consistent with epigenetic mechanisms. We have developed the following specific aims: Specific Aim 1 will be to develop a model in which human fetal liver is transplanted into nude rats and the fetal liver phenotype (defined as above) is maintained. In Specific Aim 2, we will demonstrate that manipulation of the host environment in the adult rat xenograft recipients will induce changes in fetal liver. We will examine the effects of host dietary restriction and rapamycin administration to examine the effect on fetal liver growth and gene expression. Specific Aim 3 will be to characterize and contrast the epigenetic consequences of host dietary restriction and rapamycin with the effects of arsenic exposure. The significance of this project lies in its potential to develop a model system to study mechanisms for programming of human fetal liver, something that is not possible with available methodologies.